Two-phase commit protocol (or 2PC) is a mechanism for implementing a transaction across different software components (multiple databases, message queues etc.)

3.1. The Architecture of 2PC

One of the important participants in a distributed transaction is the transaction coordinator. The distributed transaction consists of two steps:

Prepare phase — during this phase, all participants of the transaction prepare for commit and notify the coordinator that they are ready to complete the transaction

Commit or Rollback phase — during this phase, either a commit or a rollback command is issued by the transaction coordinator to all participants

The problem with 2PC is that it is quite slow compared to the time for operation of a single microservice.

Coordinating the transaction between microservices, even if they are on the same network, can really slow the system down, so this approach isn't usually used in a high load scenario.

3.2. XA Standard

The XA standard is a specification for conducting the 2PC distributed transactions across the supporting resources. Any JTA-compliant application server (JBoss, GlassFish etc.) supports it out-of-the-box.

The resources participating in a distributed transactions could be, for example, two databases of two different microservices.